Electrical filter system



p i 1932- B. F. MIESSNER 1,853,217

ELECTRICAL FILTER SYSTEM Filed Jan. 8, 1929 'HIIIlUII Patented Apr. 12,.1932 i UNITED-STATES} PATENT OFFICE,

IBENJ'AMINF. MIESSNER, OF SHORT HILLS, NEW J ERSEY,IASSIGNOR, BY MESN EASSIGN- Y IIYIENTS, TQ RADIO CORPORATION" 'OF AMERICA, OF NEW YORK, N.Y., A CORPORA- TIONOF DELAWARE ELECTRICAL FILTER SYSTEM Applicationfiled January 8, 1929. Serial No. 330,994.

The present invention relates to electrical filter systems, and'inparticular such a system forsupplying two or more loads from a singlesource of supply of periodically fluctuating uni-directional current.

A particular object is to supply the plate circuits of two or'morevacuum tubes with filtered uni-'directional'current from a S111- glerectifier ofalternating current at differcut voltages with. theeconomical use of of the loss ofcurr'ent through filter material whilekeepinghum production low, as is required in commerciallyfacceptableradio'broadcast receivers.

It is a feature of my present invention that I divide the rectified orother unsteady currentinto the number of .difierent components desiredfor distribution to work cir-,

cuits before filtration is undertaken. In present practice vfiltrationis accomplished before division takes place. For example, all of theplate current fora radio receiver having a power amplifier requiring say'200 volts, other amplifiers requiring say 100 volts, and a detectorrequiring say 40 volts, is first filtered and then divided, as by atapped resistor termed a voltage divider shunted across theroutput ofthe filter circuit, for distribution to the plate circuits ofthes'everal vacuum tubes. This practice requires a large amount offilter apparatus vandresults in a lossof some of the expensivelyfiltered current by way of the shunted voltage divider. Since it is wellknown that the-more current passing through a filter or,

in other words, the greater the load thereon,

the less complete is the filtration by reason the voltage divider,so-that the residual alternating current component after filtration islarge,thus increasing hum. In addition the voltage divider placed afterthe filter increases coupling effects between tubes and circuits atdifferent amplification levels in the system,

making oscillation prevention more difiicult.

Y Otherfeatures of the invention will be apparent from the-descriptionto follow in connection with the figures-of the drawings, in which likereference characters represent like parts: so far as possible in the twofigures. r

'Fig. 1diagrammatically.illustrates the invention ina generalized form.Fig. 2-illustrates the invention employed as afiltersystem to supply theplate circuits ofthree elec- .7

trode vacuum tubes connected in tandem in an amplifying system fromrectified alternating current.

In Fig. 1 the device S is-any source of periodically fluctuatingunidirectional ourrent, preferably shunted by a condenser C of capacitysuitable forenergy storage.v A shunt resistance B provides for dividingthe potential of the source into one orm-ore components of lesserpotential thantotal, as by connection of a circuit to the point a in theresistance as shown. The circuit including the inductance L is shownsupplyinga load IE at highest potential, andfiltration is had by theinductance of L aided by the capacity of shunt condenser 0 The circuitincluding inductance'L supplies a load IE at lower potential, and thecurrent is filtered by the inductance ofL aided by shuntcondenser Cployed for useful work is subjected to ahigh degree of filtration, theloss current through voltage divider resistance R not encountering thefilter elements at all.

The system is also adapted to coupling the coilsL and L as by winding inopposite directions on the same core, to cause the alternating currentcomponents in the two coils to oppose, to improve filtration by neutral-In this way only current emizing the fluctuating efiects. Atthe sametime such a winding provides for the magnetic field due to the directcurrent component in one circuit opposing the magnetic field due to thedirect current component in the other circuit, thus aiding in avoidingmagnetic saturation in the magnetic core, and

aiding maintaining high inductance for filtration of the fluctuatingcomponents of the currents.

In F ig. 2 a transformer T'supplied from an alternating current sourcethrough a primary winding P has secondary winding S for heating thefilament of a full wave recti 'fier tube RT, whose anodes are energizedby secondary winding S the rectified cur-,-

- rent beingsupplied to the filtersystem across the two coils.

storage condenser C and voltage divider resistance R as in the case ofFig. 1. The system supplies the plate circuits of threeelectrode vacuumtubes VT and VT connected in cascade through audio transformer T asloads corresponding to E and E respectively in Fig. 1. Transformer Tindicates an audio frequency input to the cascade amplifier, andtransformer T indicates an output, as to a loud speaker 'or othertranslating device. It is of course'understood that the amplifyingsystem may be extended, as by including a detector and one or morestages of radio frequency amplification for a usual type of radioreceiver.

Secondary windings S and S are shown to supply the filaments of tubes VTand VT respectively with raw alternating current for heating inaccordance with general practice, but any form of filament heating maybe used, this not being a feature of the present invention. ResistancesR and R connected to cross-connected filament resistances K and Krespectively, provide for developing grid bias potentials for tubes VTand VT respectively, and are further shown to have signal-shuntingcondensers C and G all in accordance with general practice, and notdirectly forming features of the present invention, so that otherarrangements suitable for accomplishing the same results may besubstituted.

Tube VT may be a power amplifier and thus supplied with high and fullpotential current through coil L filtration of coil L being aided byshunt condenser C Tube VT is shown supplied with current at lesserpotential through connection of coil L to point a on resistance R,filtration being accomplished by coil L with the aid of shunt condenserC Thus the loss current through voltage divider resistance It does notenter the filter system and, at the same time, the filter condensers Cand 0;, provide low impedance paths for the signal currents of tubes VTand VT respectively. The impedance of coils L and L cooperate with thesecondensers to prevent signal currents from reaching resistance R, andtherefore located as it is in the present invention this resistance hasnegligible eflect in producing feed-back coupling.

As in the case of Fig. 1 the coils L and L may be coupled to introduceneutralizing effects as between both the alternating and direct currentcomponent effects. Since thecurrent in L may be large compared to thecurrent in L L may have more turns in order to more nearly equalize theampereturn relation of the two coils. At the same time the values ofcondensers C and G can be selected to aid in improving the relation ofthe alternating current ampere turns in Itwill be further noted thatfluctuations in the plate circuit of tube VT will be transferred to tubeVT by way of transformer T and amplified before encountering thefluctuations in the plate circuit of VT If transformer T is so poled asto transfer the fluctuations to VT in phase to oppose the fluctuationsin the plate circuit of VT further neutralization can be had, but inview of the amplification it is desirable to have the fluctuations in VTless than in VT by a factor substantiallyequal to the amplificationfactor of VT For this reason it is desirable to filter the currentsupplied to theplate of VT to higher degree than that supplied to VT orif poor filtration is had for tube VT to make the filtration for VTcorrespondingly worse in proportion to the amplification.

The relative degrees of filtration desirable for the two tubes fits inwith the ampere-turn relation between the coils L and L A coil L oflarge number of turns will increase filtration for VT and, at the sametime, improve the ampere turn relation for neutralizing as between thetwo circuits through coupling between the coils.

Having fully described my invention, I claim: 7

1. In a current supply and filter system the combination of a source ofuni-directional periodically fluctuating current, a plurality of workcircuits, a resistance in shunt to said source to which said workcircuits are connected at points different in potential,

means associated with said work circuits in cluding an inductance coilin each circuit for filtering the currents therein independently of thecurrent lost in said resistance, said coils being so inductively relatedthat the fields generated therein by the alternating current componentsare opposed.

2. In a current supplyand filter system the combination of a source ofuni-directional periodically fluctuating current, a plurality of workcircuits, means for impressing from said source currents at differentpotentials upon said work circuits, and inductance coils in two of saidcircuits so inductively related that the fields generated therein by thealternating current components are opposed.

3. In an amplifying system including three electrode vacuum tubesconnected in cascade, a current supply and filter system for energizingthe plate circuits of said tubes comprising a source of uni-directionalperiodically fluctuating current, a resistance in shunt to said sourceto which the plate circuits of said tubes are connected at pointsdifferent in potential, and means associated with said plate circuitsfor filtering the currents delivered thereto, said means includinginductance coils in two of said circuits so therein are opposed.

4. In an electrical system, the combination of a source of rectifiedalternating current, a a plurality of work circuits, a storage condenseracross said source, a voltage divider resistance connected across saidcondenser, a plurality of work circuits, a plurality of filter systems,each system including an inductance connected between said resistanceand one of said work circuits, and a plurality of condensers connectedbetween the connection of said inductances to said Work circuits and theother terminal of said resist ance, said inductances being coupledtogether and so poled that the magnetic flux of each of said inductancesdue to the direct current flowing therethrough to any work circuit andthe alternating current component of the current flowing through one ofsaid .in-e

ductances is materially reduced.

5. In an amplifying system, a plurality of space discharge devices, acurrent supply and filter system for energizing the anode circuits ofsaid devices comprising a source of unidirectional fluctuating current,a resistance element shunted across said source to which the anodecircuits of said devices are connected at points different in potentialand means associated with said anode circuits for filtering the currentsdelivered thereto, said means including inductance coils in twojof saidcircuits wound around the same core and so inductively related that thefields generated therein are opposed whereby fluctuating current effectsin each of said circuits are substantially neutralized and magneticsaturation of said core is substantially prevented.

In witness whereof, I have hereuntosub scribed my name this 5th day ofJanuary,

BENJAMIN r. MIEssNER.

